Manufacture of safety razor blades



Feb. 5, 1935. o. ROTH 1,989,886M

MANUFACTURE OF SAFETY RAZOR BLADES Filed April 18, 1933 a a J'Q M 4 m mm 'JA/VZ/VTOR @fra-%% Patented Feb. 5, 1935- UNITED STATES PATENT OFFICEMANUFACTURE OF SAFETY RAZOR BLADES Application April 18, 1933, SerialNo. 666,641

A 7 Claims. The present invention relates to the manufacture of safetyrazor blades of the thin flexible type havingac'ontinuous slot ofsubstantial length, e. g., extending substantially over the whole length,5 of the cutting edge of the blade, and having end portions which areintended to be bent transversely and maintained in a position ofcurvature during use, and whose medial parts are substan' tially softerthan the cutting edges.

With known methods of producing such blades it is difllcult to obtainthe desirable degree of hardnessof the cutting edges, if the medial areais to be sufliciently soft to permit the blade to flex without risk offracture. Moreover such prior methods are very liable to producedistortion of such blades so as to render it commercially impracticableto produce therefrom finished bladeswith an even cutting edge bygrinding in the strip. a

The object of the presentinvention is to facilitate obtainingdifferential hardening, and to enable the manufacturer to obtain moreeasily such different conditions of edge and medial hardness as he maydesire.

What are the optimum conditions is to some extent a matter of opinion.It has been found that a blade with an edge hardness of about 850 i onthe Vickers hardness testing machine and a hardness of 650 or less nearthe medial projec- 30 tions gives good results in practice, but itshould be observed that with these blades it a matter of greatdifllculty to obtain exact figur'es.

The new process is characterized by the employment of an electriccurrent in connection with 35 a blade of such configuration andproportion that there is a substantial diiferenee between the density ofthe current flow in difierent portions of the blade, the greatestdensity of such flow being in the end portions where the metal should 40be of ,the lowest degree of hardness, and least density at and near thecutting edge, the heating eil'ect at each point being proportional toPR, where I is the density-of the current flow at such point and R theresistance.

45 To obtain this differential density the current is applied to ahardened bladehaving a medial slot of substantial length, and endportions so shaped that the breadth of metal available for the passageof the current through such end portions is substantially less than thatso available in the medial portion of the blade, whereby the density ofthe current flow in such end portions is increased beyond that near thecutting edges.

The length of the slot has an important effectinproducingthisresultashasalsoitstermi- Great Britain May 13, 1932 nal form. With aslot of substantially even breadth and the current entering and leavingat the ends of the blade the density of the current flow' near themedial line of the blade will also tend to be somewhat greater than ator near the cutting edge, since the path from electrode to electrode isless near such medial line.

I The process is applicable to blades of known shape, e. g., such asthose shown in U. S. Letters Patent Nos. 1,869,327, 1,850,902 and1,858,316 since the end portions of such blades possess the requisitequalities above described.

The method is applicable both to,cases where blades are hardened and/0rtempered in the strip, and where individual blades are hardened and/ortempered separately.

The present invention is particularly suited forv ered to leavesubstantially equal portions. thereof on adjacent blades.

, The process may be carried out by first subjecting the strip to anyknown hardening process and then subjecting it to the electricaltreatment by which the blade is tempered so as to give the desired edgehardness and the less hardened end portions simultaneously.-

Owing to the fact that the end portions of the blade atwhich the currententers and leaves are of less cross sectional area than the main portionof the blade the current density will be substantially greater at theend areas than along the main portion of the blade, whereby such adifferential tempering is obtained between the end areas and the mainportion of the blade as will give the blade the characteristicshereinbefore referred to.

In order that the invention may be the more readily understood referenceis hereinafter made. to the accompanying drawing, in which:-

Fig. 1 is adiagrammatic view of one form of apparatus for carrying outthe present process, and

Fig. 2 shows part of a strip of blade blanks adapted to be treated bythe process.

Referring to the drawing, the strip of blade blanks a after beinghardened by passingthrough a hardening apparatus 1 is caused to bridge agap in an electric circuit, so that with a blade having a longitudinalslot the current will divide into two parts between the successivenecks.

- For this purpose the strip passes to the electrical treatmentapparatus comprising spaced apartpairs of contact blocks 9, 9a and 10,10a. The blocks are held to the strip by light spring pressure so thatthey form yielding clamp contacts. The blocks 10, 100. are water cooled,a. part of the water cooling system being indicated by 11. The water inthe blocks 9, 9a is preferably insulated from the contacts.

The blocks 9, 9a and 10, 10a are units an open circuit 11a, havingtherein a variable re stanc'e 12, a single pole switch 13, an ammeter'14, and the secondary winding 15 of a transformer, the primary winding16 being connected to the mains by a double pole switch 17. 18 is avolt: meterconnected across the circuit 11. The circuit 11 is closed bythat part of the strip which for the time being bridges the gap betweenthe contact blocks 9, 9a and 10, 10a.

A .working example of voltage and amperage for a strip in which theblades are proportioned as shown each blade being about 43 mm. long is20 volts, 40 amps, with 40 blades between the contacts, the speed ofstrip going through being 200 blades a minute.

The strength of the current is so chosen with respect to the rate offeed of the strip, and the distance the contacts are spaced apart,that'in the time that the blade is subject to the heating effect of thecurrent the necks c are softened the desired amount, while reducing theedge hardness I of the strip to that desired.

By the present invention the following factors,

rent near the ends compared to that of other portions of the blade, andby experiment or calculation these factors can be so varied as to obtaina great variety of differences of temper.

Further, where the current is applied to a strip containing a number ofblades, the differentiation of current density may be increased bynicking or the like, so that the breadth of the parts by which thecurrent enters or through which it flows is decreased. Nicks d at thenecks between the blades are shown in Fig. 2.

Apart from the specific advantages above described the use of theelectric current avoids many of the difliculties attached to othermethods of tempering.

What I claim is:- 1. Process for the production of thin flexible razorblades with high edge hardness and relatively softer medial end areas,comprising applying an electric current to a hardened blade having amedial slot of substantial length, the cross sectional area of the endportions of such blade being substantially less than that of theintermediate portion so that the density of the current is substantiallygreater over the medial end portions than at or nearv the cutting edges.

2. Process for the production of thin flexible razor blades with highedge hardness and relatively softer medial end areas, which comprisesapplying an electric current to a hardened strip of blades whichareprovided with a longitudinal slot of 'substantiallength, the portions ofsuch stripbetween the slots being of substantially less cross sectionalarea than that of the remaining part of the strip so that the density ofthe current is substantially greater over the medial end portions of theblades than at or near the cutting,

edges.

3. Process for the production of thin flexible razor blades with a highedge hardness and relatively softer medial end areas, comprisingapplying an electric current to a plurality of hardened blades which areprovided with a longitudinal slot of substantial length and are eachconnected longitudinally in strip form by necks of substantially lesscross-sectional area than the main portion of the blade so that thedensity of the current will be substantially greater over'the medial endportions of the blades than at or near the cutting edges.

4. Process for the production of thin flexible razor blades with a highedge hardness and relatively softer medial end areas, which consists inhardening a plurality of blades which are each provided with alongitudinal slot of substantial length and are connected longitudinallyin strip formby necks of substantially lesscross-sectional area than themain portion of the blade, and then applying an electric current to suchstrip so as simultaneously to temper the blades and to reduce to agreater extent the hardness of the necks by the differential currentdensity set up along the strip.

5. Process for the production of thin flexible razor-blades with a highedge hardness and relatively softer medial end areas, comprisingapplying an electric current to a plurality of hardened blades which areeach' provided with a longitudinal slot of substantial length and areconnected longitudinally in strip form by necks of substantially lesscross-sectional area than the main portion of the blade so that thedensity of the current will be substantially greater over the medial endportions of the blades than at or near the cutting edges, the saidcurrent entering and leaving through externally cooled electrodes.

6. Process for the production of thin flexible razor blades with highedge hardness and relatively softer medial end areas, comprisinghardening a blade having a medial slot of substantial length and thenapplying an electric current to the blade so as simultaneously to temperthe bladeat or near the cutting edges and reduce to a greater extent thehardness of the medial end areas of the blade, the cross-sectional areasof the end portions of'such'blade being substantially less than that ofthe cutting portion so that the density of the current is substantiallygreater over the medial end areas than at or near the cutting edges.

7. Process for the production of thin'flexible razor blades with highedge hardness and relatively softer medial end areas, comprisingapplying an electric current to a hardened blade having a medial slot ofsubstantial length, thecrosssectional area of each end portion of suchblade being substantially less than the combined crosssectional area ofthe cutting-edge-bearing portions'so that the density of the current issubstantially greater over the medial end portions than at or nearthecutting edges.

. OTTO ROTH.

